I've supplemented a nutrient tea made of compost with goldfish without issue. I've also read of people using it in bigger aquaponic as well. What are you trying to clean? Beneficial bacteria should keep the system clean of slime, you don't necessarily need fish for that. Keeping the light out of the res should keep it clear of algae. I use that black/white poly with the white side facing out to keep light out. My system was small too, I find it much easier to go the organic route without fish, one less thing to worry about.